1. Field of the Invention
The present invention relates to a pressure adjusting device, and more particularly, to a pressure adjusting device for controlling the pressure within the ink reservoir of an ink-jet print cartridge.
2. Description of the Prior Art
With the increasing in popularity of personal computers, and a correspondingly increasing demand for personal image output, ink-jet printing devices have become the most common computer output/printing devices for individuals, families, and companies. Such devices offer a price and printing quality that is attractive for users. Ink-jet printing generally relies on the controlled delivery of ink droplets from an ink-jet print cartridge ink reservoir to a print medium. Among the printing methods for delivering these ink droplets from the ink reservoir to the print head, drop-on-demand printing is a commonly used method. The drop-on-demand method typically uses thermal bubbles or piezoelectric pressure wave mechanisms. The thermal bubble type print head comprises a thin-film resistor that is heated to cause sudden vaporization of a small portion of the ink. The vapid expansion of the ink vapor forces a small droplet of ink through a print head nozzle. Although drop-on-demand printing is ideal for sending ink droplets from an ink reservoir to the print head, some mechanisms must be included to prevent ink from leaking out of the print head while the print head is inactive. This kind of controlling mechanism usually provides a slight back-pressure at the print head to prevent ink from leaking out from the print head whenever the print head is inactive. The term xe2x80x9cback-pressurexe2x80x9d indicates a partial vacuum within the ink reservoir. The back-pressure is defined in a positive sense so that increasing the back-pressure means that the degree of partial vacuum has increased within the ink reservoir.
Although increasing the back-pressure can prevent ink from leaking out from the print head, the back pressure must not be so high that the print head can not overcome the back-pressure to eject ink droplets. Furthermore, as ambient air pressure decreases, the necessary back pressure that prevents ink from leaking out from the print head needs to be correspondingly larger. Accordingly, back-pressure within the ink-jet print cartridge has to be regulated whenever the ambient pressure drops. Also, the pressure within the ink reservoir is subjected to what may be termed xe2x80x9coperational effectsxe2x80x9d. This refers to the depletion of ink from the ink reservoir, which tends to increase the back-pressure within the ink reservoir. Unless the back-pressure is regulated properly, the print head will eventually fail because the back-pressure becomes too great for the print to overcome.
In the prior art, a xe2x80x9cregulatorxe2x80x9d in the ink reservoir controls the reservoir back-pressure. The regulator is usually an elastic air bag, and the elastic air bag typically connects to the external atmosphere via a vent. When ink is consumed, for example, ambient air will enter into the elastic air bag through the vent so that the volume of the elastic air bag increases to decrease the reservoir volume, and so reduce the back-pressure to a value that is within the operational range of the print head. Another example can be found in a drop of ambient pressure. In such cases, the volume of the elastic air bag changes to increase the reservoir volume to thereby increase the back-pressure to a level that prevents ink leakage from the print head.
A major shortcoming of the prior art elastic-air-bag regulator is a limitation in a maximum volume of the elastic air bag. As ink is gradually jetted from the print head, the elastic air bag will eventually reach its maximum extent, and the reservoir volume can therefore not be adjusted further. The continuous reduction of ink volume in the reservoir causes the back-pressure to exceed the operational back-pressure range. When this occurs, the print head can no longer overcome the back-pressure to eject ink from the print head, and the remaining ink within the ink reservoir cannot be used completely and so is wasted.
Another type of prior art that is used to control the back-pressure within an ink reservoir is a bubble generator. As disclosed in U.S. Pat. No 5,526,030, which is included herein by reference, the bubble generator is set in the ink reservoir and has an orifice through which ambient air can enter the reservoir. The dimensions of the orifice, when designed appropriately, cause ink to gather in the orifice to seal off the reservoir by way of capillary effects. When the back-pressure within the ink reservoir rises to a predetermined degree, external air overcomes the liquid seal and enters into the ink reservoir as a bubble. Thus, the back-pressure within the ink reservoir decreases. Additionally, when the bubble enters into the ink reservoir, capillary effects again take over and re-establish the liquid seal to prevent bubbles from continuously entering. However, the bubble generator described above uses surface the tension of the ink and static pressure of the ink column to control bubbles entering the ink reservoir. Therefore, the primary shortcomings of the prior art described above are: 1. Different inks have different surface tensions, and so the bubble generator needs to be redesigned for various types of ink; 2. As the level of ink within the reservoir gradually drops, the static pressure of the ink column decreases, leading to the entrance of air bubbles at smaller back pressures; 3. The gap between the sphere and the orifice has to be precisely engineered to permit the entrance of air bubbles at the correct reservoir back-pressure. This increases difficulties in fabricating the reservoir of an ink-jet cartridge.
It is therefore a primary objective of the present invention to provide a pressure adjusting device capable of controlling the pressure within the ink reservoir of an inkjet cartridge.
Another objective of the present invention is to provide a simple and reliable pressure adjusting device.
According to claimed invention, an ink-jet cartridge comprises an ink reservoir for storing ink. The reservoir has a first vent, a second vent, and an opening. The opening is installed at a bottom end of the reservoir and is connected to the print head. An air bag is installed within the ink reservoir and connected to the first vent. The first vent enables external air to enter into the air bag, enabling the air bag to adjust internal pressure within the ink reservoir. An elastic constraining device is installed in the ink reservoir for constraining air in the air bag, and so to prevent the ink in the ink reservoir from leaking through the opening. An active shaft is movably installed in the ink reservoir. A plugging device engages with the active shaft to plug the second vent of the housing. Consumption of the ink within the ink reservoir causes the air bag to expand. When the air bag expands to a predetermined degree, the air bag moves the active shaft, the active shaft pulls the plugging device out of the second vent, and air enters into the ink reservoir through the second vent to reduce the volume of the air bag. When the air bag steps moving the active shaft, the active shaft returns to an original position and the plugging device plugs the second vent again.
It is an advantage of the present invention that the pressure adjusting device can adjust internal pressure within the ink reservoir.
It is a further advantage of the present invention that the structure is simple and reliable. Even if ambient air pressure changes, it still works normally and isn""t affected by operational effects of the ink reservoir.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.